Morphological evidence suggests that membrane-coating granules arise from the Golgi Apparatus in stratum spinosum cells and are subsequently discharged from stratum granulosum cells into the intracellular spaces. Our ultimate objective is to isolate the membrane-coating granules from rat gingival epithelium, to define their biochemical composition and activities, and to elucidate their role in the keratinization process. Since ultrastructural studies indicate that membrane-coating granules alter plasma membranes, the first stage of this project involves establishing an isolation procedure for both membrane-coating granules and the plasma membrane fraction(s) of the keratinizing epithelial cells. Keratinizing epithelia from a variety of sources will be used individually and in combination to establish minimum amounts of starting material for homogenization, centrifugation, and assays. Afterwards, studies will concentrate on gingival epithelium. Homogenization procedures and density-gradient centrifugation steps will be constantly monitored by both light microscopy and transmission electron-microscopy. Subsequent biochemical analyses of isolated membrane-coating granules and the plasma membrane fraction(s) may reveal possible mechanisms involved in the development of the impermeable-barrier membrane of the stratum corneum cell. Such information defining primary biochemical events involved in the normal differentiation process of keratinization could contribute greatly to understanding parakeratotic and dyskeratotic conditions such as leukoplakia and carcinoma.